Electronic device manufacturers strive to produce a rich interface for users. Conventional devices use visual and auditory cues to provide feedback to a user. In some interface devices, kinesthetic feedback (such as active and resistive force feedback) and/or tactile feedback (such as vibration, texture, and heat) is also provided to the user, more generally known collectively as “haptic feedback” or “haptic effects”. Haptic feedback can provide cues that enhance and simplify the user interface.
Haptic feedback has been implemented on rotary knobs and other types of electromechanical devices such as mechanical switches and encoders to create a flexible user interface. A wide variety of available haptic feedback, including detents, barriers and vibrations provide the user with advantages in usability, design and cost.
Generally, haptic feedback is generated on a rotary knob with a motor-based actuator system or a braking-based actuator system. A motor-based actuator system applies a force to either oppose or to reinforce a user's motions. However, because a motor always adds energy to the system, it can become unstable. Further, a motor-based actuator system requires a relatively large and costly motor to generate the required amount of torque.
In contrast, a braking-based actuator system uses braking actuators that dissipate energy and resist user motion through friction. A braking-based actuator system is generally smaller and less expensive than a motor-based actuator system and does not become unstable since it takes energy out of the system.
One problem with known rotary knobs having a braking actuator system is that a magnetic air gap must be maintained between two metallic rigid devices. This air gap must typically be maintained within a tight tolerance, thus making manufacturing of the device expensive and difficult. Further, known rotary knobs with braking actuators typically only include one level of frictional braking. However, some desired haptic feedback is more effective if it includes multiple levels of frictional forces.
Based on the foregoing, there is a need for an improved frictional braking actuator system.